Process for the electrolytic production of zinc.



No. 831,843. PATENTED SEPT. 25, 1906.

V. ENGELHARDT. I PROCESS FOR THE ELECTROLYTIC PRODUCTION OF ZINC.

APPLICATION FILED SEPT.14, 1904.

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VICTOR ENGELHARDT, OF VIENNA, AUSTRIA-HUNGARY, ASSIGNOR SIEMENS & HALSKE AKTIENGESELLSCHAFT, OF BERLIN, GERMANY.

PROCESS FOR THE ELECTROLYTIC PRODUCTION OF ZINC.

Specification of Letters Patent.

Patented. Sept. 25, 1906.

Application filed September 14,1904. Serial No. 224,365.

To all whom it may concern.-

Be it known that I, VICTOR ENGELHARDT, a subject of the Emperor of Austria-Hun ary, residing in Vienna, Austria-Hungary, ave invented a new and useful Process for the Electrolytic Production of Zinc; and in order that others skilled in the art may understand and practice my invention I give the following specification.

My invention relates to the production of zinc by the electrolysis of solutlons of sulfate of zinc, and has for its object the production of a crystalline dense smooth electrolytic zinc free from sponginess and roughnesses or irregularities of surface.

In the accompanying drawings I have illustrated one form of. anode by which my invention may be attained.

Figure 1 of said drawin s shows a face view of an anode. Fig. 2 s ows a sectional view thereof.

Processes heretofore known for the electrolytic roduction of zinc from solutions of zinc sul ate in which insoluble anodes were employed resulted in the formation of spongy zinc, and the zinc deposit so obtained was injuriously affected by the sulfuric acid liberated at the anode.

The spongy-zinc de osits resulted, amon other causes, from t e influence of smal quantities of impurities in the solutions which came from the raw materials used or from the anodes. These impurities (iron, manganese, lead, copper, &c.) were precipitate upon the cathode and gave rise there to secondary reactions. A further cause of the formation of s ongy-zinc de osits is the formation of zinc ydrogen at t e cathodes.

The sulfuric acid enerated at the anode acts u on the catho e de osit by redissolving' t e already electro ytically-deposited zinc, particularly at the higher acid concentrations or where there is excess of acid, as wherethe zinc deposition has far advanced or where there is impoverishment of the bath in zinc.

My invention is directed to the elimination and overcoming of the above disadvanta es.

It consists in the em loyment in the e ectrolysis of a current ensity for the Whole surface of the insoluble anode or for separate portions thereof, which is considerably greater than that at the cathode. I have ascertained that a current density at the Thus for practically obtainable zinc concen trations in which a current density at the cathode of about one hundred and fifty amperes per square meter of the cathode-surface. is employed the current density at the anode either for the whole surface or at single places of the same would be from three thousand to seven thousand five hundred amperes per square meter of the surface. These figures are cited as examples merel without in any way limiting the invention t ereto;

The form of the anode is a matter of minor importance; but it is important that it Works for its whole surface or for single places thereon with a current density con'slderably higher than at the cathode. For this purpose an anode-surface is selected having the necessary smaller dimensions, or an' anode is selected of a surface equal to the cathode which is reinforced at several places as, for exam le, by bands, ribs, or Wire insertions, as indicated in the drawingsso that at these places a higher conductivity is produced, and therefore a higher current density obtained.

In the drawings an anode is shown provided with a series of stri s or bands 1 1 2 2 of material of higher conductivity than the remainder of the anode, so that at the places occupied by the bands a higher current density is obtained.

A further important feature ofmy invention consists in the availability of the employment of platinum or its alloys as the anodes in the electrolytic roduction of zinc.

such materials has been out of the question on account of the expense involved. In accordance with my invention, however, the anodes are of such small size that latinum or latinum alloys can be used wit out materially increasing the cost of the electrolytic zinc by the loss of the anode material.

I am aware that it has been roposed in electrolytic processes to use ano es of some what smaller dimensions than the cathodes, the latter extending beyond the edges of the anodes. This pro osition, however, is merely for the urpose of avoiding the formation of burs or obs or roughnesses on the edges of the cathodes, and, moreover, this process merely results in an increase of the current density at the anode of only a small percent- In connection with .elctrometallurgical processes the employment of a considerable difference of current density between the electrodes is of great advantage and importance, and particularly in the case of the electrolysis of zinc-sulfate solutions, because [.0 of the improvement in the deposit obtained. By this new process I am enabled to produce --acrystalline perfectly dense smooth zinc de posit free from s onigness and roughness or irregularities an "resembling in its outer appearance electrolytically refined co per. These results may be explained as fol ows: By increasing the current density at the anode the formation of ozone and supersulfuric acid is materially promoted, and these have an oxidizing effect upon the cathode or zinc hydrogen. Moreover, my invention renders possible the employment of anodes ofplatinum orplatinum alloys, and thus the tendency of thefbath to become impure duringthe electrolysisby particles coming from the anodes is effectively prevented. The chemical purity jef thedepesit has the furthzerfand deeir able dissolvin actiono the sulfuric acid which becomes eat the anode.

"Having described my" invention, what 1 claim, and desire toprotect by Letters Patentis f1. The process for the electrolytic produc- 3 5 tion of iz'ilfcfromisjlilfatesolutions, which consists-in em loyin "a cur ent density at the anode which is su stantially' twenty or more times the current density atthe cathode.

f'j 2*; flhe process forjthe electrolytic produc- 4u tion of from sulfate solutions which conropertyof resisting the anode a current eater than the current density 75 at the catho e.

sists in employing at the anode a current density of from twenty to fifty times that of the current density at the cathode, substantially as and forthe purposes described. 4

3. The process for the electrolytic production of zinc from sulfate solutions, which consists in employing an insoluble anode, and a current density at said anode substantially twenty or more times the current density at the cathode. v

V 4. The process for the electrolytic production of zinc from sulfate solutions, which con-- sists in em loying an anode of platinum or platinum a loy and a current density at said i anode which is substantially twenty or more times the current density at the cathode.

5. The process for the electrolytic production of zinc from sulfate solutions which consists in employing an insoluble anode and a current density at said anode of from twenty to fifty times that of the current density at the cathode, substantially as and for the purposes described.

6. The process for the electrolytic production of zinc from sulfate solutions which consists in employing an'anode of platinum or platinum a loy and a current density at said anode of from twenty to fifty times that of the current density at the cathode, substantially as and for the purposes described.

7. The process for the electrolytic produc- :tion of zinc from sulfate solutions, which consists in employingi at separate places on the ensity which is twenty or more times VICTOR ENGELHARDT.

Witnesses:

ALvEs'ro S. HOGUE, Aueus'r FUGGER. 

